Notify policy of untrusted touch for toast

Notify policy when an untrusted touch happens with the obscuring package
so we can show a toast in topic CL.

Test: Enable feature, draw overlay, verify toast appears
Test: atest WindowUntrustedTouchTest WindowInputTests inputflinger_tests
      inputflinger_benchmarks libinput_tests libgui_test
Bug: 158002302
Change-Id: Ief4a048128efc52b505a1a8c60aa2240a196f254